Thailand, like many developing nations, is facing a wide range of environmental challenges, many of which are caused by industrial pollution. The country has found that traditional command and control legislation is not effectively tackling this problem. It is therefore promoting various voluntary environmental programmes as a way for businesses to improve their environmental performance. To provide more information on the effectiveness of this approach, and to see how to maximize its impact, this study has assessed the implementation of one of the most popular voluntary environmental schemes, ISO 14001. This study finds that firms sign up to ISO 14001 for a number of reasons, the most important being the impetus provided by their management policies, the need to boost corporate image and the desire to socially responsible.  The study proposes a number of policies to help firms to adopt the voluntary scheme. These include providing financial incentives and helping firms with training and provision of information and technical advice.